{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,27]],"date-time":"2026-09-27T08:17:35Z","timestamp":1790497055066,"version":"4.1.0"},"reference-count":50,"publisher":"Wiley","issue":"11","license":[{"start":{"date-parts":[[2018,2,7]],"date-time":"2018-02-07T00:00:00Z","timestamp":1517961600000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"}],"funder":[{"name":"National Cancer Institute at the National Institutes of Health","award":["R01 CA052449"],"award-info":[{"award-number":["R01 CA052449"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Intl Journal of Cancer"],"published-print":{"date-parts":[[2018,6]]},"abstract":"<jats:p>Receptor\u2010defined subtypes of breast cancer represent distinct cancer types and have differences in risk factors. Whether the two main hormonal forms of oral contraceptives (OCs); i.e. progestin\u2010only (POC) and combined oral contraceptives (COC), are differentially associated with these subtypes are not well known. The aim of our study was to assess the effect of POC and COC use on hormone receptor\u2010defined breast cancer risk in premenopausal women in a prospective population\u2010based cohort \u2013 The Norwegian Women and Cancer Study (NOWAC). Information on OC use was collected from 74,862 premenopausal women at baseline. Updated information was applied when follow\u2010up information became available. Multiple imputation was performed to handle missing data, and multivariable Cox regression models were used to calculate hazard ratios (HR) for breast cancer. 1,245 incident invasive breast cancer cases occurred. POC use \u22655 years was associated with ER+ (HR\u2009=\u20091.59, 95% CI 1.09\u2013 2.32, <jats:italic>p<\/jats:italic><jats:sub>trend<\/jats:sub>\u2009=\u20090.03) and ER+\/PR+ cancer (HR\u2009=\u20091.63, 95% CI 1.07\u20132.48, <jats:italic>p<\/jats:italic><jats:sub>trend<\/jats:sub>\u2009=\u20090.05), and was not associated with ER\u2212 (<jats:italic>p<\/jats:italic><jats:sub>heterogeneity<\/jats:sub>\u2009=\u20090.36) or ER\u2212\/PR\u2212 (<jats:italic>p<\/jats:italic><jats:sub>heterogeneity<\/jats:sub>\u2009=\u20090.49) cancer. COC use was associated with ER\u2212 and ER\u2212\/PR\u2212 cancer, but did not increase risk of ER+ and ER+\/PR+ cancer. Current COC use gave different estimates for ER\/PR\u2010defined subtypes (<jats:italic>p<\/jats:italic><jats:sub>heterogeneity<\/jats:sub>\u2009=\u20090.04). This is the first study to show significant associations between POC use and hormone receptor\u2010positive breast cancer. The lack of power to distinguish effects of POC use on subtype development calls for the need of larger studies to confirm our finding.<\/jats:p>","DOI":"10.1002\/ijc.31266","type":"journal-article","created":{"date-parts":[[2018,1,19]],"date-time":"2018-01-19T05:42:42Z","timestamp":1516340562000},"page":"2293-2302","source":"Crossref","is-referenced-by-count":37,"title":["Progestin\u2010only and combined oral contraceptives and receptor\u2010defined premenopausal breast cancer risk: The Norwegian Women and Cancer Study"],"prefix":"10.1002","volume":"142","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-5767-3204","authenticated-orcid":false,"given":"Marit","family":"Busund","sequence":"first","affiliation":[{"name":"Department of Community Medicine UiT The Arctic University of Norway 9037 Troms\u00f8 Norway"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Nora S.","family":"Bugge","sequence":"additional","affiliation":[{"name":"Department of Community Medicine UiT 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